diff --git a/core/src/main/java/com/google/adk/tools/SetModelResponseTool.java b/core/src/main/java/com/google/adk/tools/SetModelResponseTool.java
index dad84a73b..4f7022914 100644
--- a/core/src/main/java/com/google/adk/tools/SetModelResponseTool.java
+++ b/core/src/main/java/com/google/adk/tools/SetModelResponseTool.java
@@ -37,10 +37,7 @@
 public class SetModelResponseTool extends BaseTool {
   public static final String NAME = "set_model_response";
 
-  // Prefix of the SchemaUtils validation message after which the full schema is appended. Used to
-  // strip the schema dump from feedback on a best-effort basis; if SchemaUtils changes its wording
-  // the feedback simply stays unstripped. runAsync_unknownArg_feedbackOmitsSchemaDump pins the
-  // current format.
+  // Marker after which SchemaUtils appends the schema dump; stripped from feedback best-effort.
   private static final String OUTPUT_SCHEMA_DUMP_MARKER = " does not match agent output schema: ";
 
   private final Schema outputSchema;
@@ -92,21 +89,22 @@ private static Map<String, Object> excludeNullFields(Map<String, Object> values)
     for (Map.Entry<String, Object> entry : values.entrySet()) {
       Object value = entry.getValue();
       if (value != null) {
-        result.put(entry.getKey(), excludeNullFields(value));
+        result.put(entry.getKey(), excludeNullsFromValue(value));
       }
     }
     return result;
   }
 
-  @SuppressWarnings("unchecked")
-  private static Object excludeNullFields(Object value) {
+  private static Object excludeNullsFromValue(Object value) {
     if (value instanceof Map<?, ?>) {
-      return excludeNullFields((Map<String, Object>) value);
+      @SuppressWarnings("unchecked") // Function-call args always have String keys.
+      Map<String, Object> map = (Map<String, Object>) value;
+      return excludeNullFields(map);
     }
     if (value instanceof List<?>) {
       List<Object> result = new ArrayList<>();
       for (Object item : (List<?>) value) {
-        result.add(excludeNullFields(item));
+        result.add(excludeNullsFromValue(item));
       }
       return result;
     }
diff --git a/core/src/test/java/com/google/adk/flows/llmflows/OutputSchemaTest.java b/core/src/test/java/com/google/adk/flows/llmflows/OutputSchemaTest.java
index ad0e97df6..d9dbfed0a 100644
--- a/core/src/test/java/com/google/adk/flows/llmflows/OutputSchemaTest.java
+++ b/core/src/test/java/com/google/adk/flows/llmflows/OutputSchemaTest.java
@@ -183,7 +183,8 @@ public void getStructuredModelResponse_withValidationFeedback_returnsEmpty() {
             .response(
                 ImmutableMap.of(
                     "error",
-                    "Validation Error found: field1 is required. Fix the errors and call it again."))
+                    "Validation Error found: field1 is required. Fix the errors and call it"
+                        + " again."))
             .build();
     Event event =
         Event.builder()
@@ -365,19 +366,19 @@ public BaseLlmConnection connect(LlmRequest llmRequest) {
     // The retry request must carry the validation feedback from the first call back to the model:
     // the feedback names the missing required field, tying it to the first call's failure.
     assertThat(scriptedLlm.getRequests()).hasSize(2);
-    boolean feedbackSentBack =
+    Optional<String> feedbackError =
         scriptedLlm.getRequests().get(1).contents().stream()
             .flatMap(content -> content.parts().orElse(ImmutableList.of()).stream())
             .map(Part::functionResponse)
             .flatMap(Optional::stream)
-            .anyMatch(
-                fr ->
-                    Objects.equals(fr.name().orElse(""), SetModelResponseTool.NAME)
-                        && fr.response().orElse(ImmutableMap.of()).get("error")
-                            instanceof String error
-                        && error.contains("Validation Error found")
-                        && error.contains("field1"));
-    assertThat(feedbackSentBack).isTrue();
+            .filter(fr -> Objects.equals(fr.name().orElse(""), SetModelResponseTool.NAME))
+            .map(fr -> fr.response().orElse(ImmutableMap.of()).get("error"))
+            .filter(String.class::isInstance)
+            .map(String.class::cast)
+            .findFirst();
+    assertThat(feedbackError).isPresent();
+    assertThat(feedbackError.get()).contains("Validation Error found");
+    assertThat(feedbackError.get()).contains("field1");
 
     // Only the corrected, validated response becomes the final structured output.
     Event finalEvent = events.get(events.size() - 1);